contains method
Checks if the given offset is within this selection.
Returns true if offset is between startOffset and endOffset (inclusive).
Example:
final sel = ByteSelection.range(5, 10);
sel.contains(7); // true
sel.contains(5); // true (inclusive)
sel.contains(10); // true (inclusive)
sel.contains(11); // false
Implementation
bool contains(int offset) {
return offset >= startOffset && offset <= endOffset;
}